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docd replicate and sql query changes 

git-svn-id: https://svn.jboss.org/repos/hibernate/trunk/Hibernate3/doc@5697 1b8cb986-b30d-0410-93ca-fae66ebed9b2
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Gavin King 2005-02-13 05:38:20 +00:00
parent 3e8ea3cdac
commit 8f557f26ff
2 changed files with 151 additions and 71 deletions
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128
reference/en/modules/query_sql.xml
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@ -3,79 +3,90 @@
<para>
You may also express queries in the native SQL dialect of your database. This is useful if you
want to utilize database specific features such as the CONNECT keyword in Oracle.
This also allows for a cleaner migration path from a direct SQL/JDBC based application to
Hibernate.
want to utilize database specific features such as query hints or the <literal>CONNECT</literal>
keyword in Oracle. It also provides a clean migration path from a direct SQL/JDBC based
application to Hibernate.
</para>
<para>
Hibernate3 also supports native SQL statements for all create, update, delete, and load
Hibernate3 allows you to specify handwritten SQL for all create, update, delete, and load
operations.
</para>
<sect1 id="querysql-creating">
<title>Creating a SQL based <literal>Query</literal></title>
<title>Creating a native SQL <literal>Query</literal></title>
<para>
SQL queries are exposed through the same <literal>Query</literal> interface, just like ordinary
HQL queries. The only difference is the use of <literal>Session.createSQLQuery()</literal>.
SQL queries are controlled via the <literal>SQLQuery</literal> interface, which
is obtained by calling <literal>Session.createSQLQuery()</literal>.
</para>
<programlisting><![CDATA[Query sqlQuery = sess.createSQLQuery("select {cat.*} from cats {cat}", "cat", Cat.class);
sqlQuery.setMaxResults(50);
List cats = sqlQuery.list();]]></programlisting>
<programlisting><![CDATA[List cats = sess.createSQLQuery("select {cat.*} from cats cat")
.addEntity("cat", Cat.class);
.setMaxResults(50);
.list();]]></programlisting>
<para>
The three parameters provided to <literal>createSQLQuery()</literal> are:
This query specified:
</para>
<itemizedlist>
<listitem>
<para>
the SQL query string
the SQL query string, with a placeholder for Hibernate to inject the column aliases
</para>
</listitem>
<listitem>
<para>
a table alias name
</para>
</listitem>
<listitem>
<para>
the persistent class returned by the query
the entity returned by the query, and its SQL table alias
</para>
</listitem>
</itemizedlist>
<para>
The alias name is used inside the sql string to refer to the properties of the mapped class
(in this case <literal>Cat</literal>). You may retrieve multiple objects per row by supplying
a <literal>String</literal> array of alias names and a <literal>Class</literal> array of
corresponding classes.
The <literal>addEntity()</literal> method associates SQL table aliases with entity classes,
and determines the shape of the query result set.
</para>
<para>
The <literal>addJoin()</literal> method may be used to load associations to other entities
and collections. TODO: examples!
</para>
<para>
A native SQL query might return a simple scalar value or a combination of scalars and
entities.
</para>
<programlisting><![CDATA[Double max = (Double) sess.createSQLQuery("select max(cat.weight) as maxWeight from cats cat")
.addScalar("maxWeight", Hibernate.DOUBLE);
.uniqueResult();]]></programlisting>
</sect1>
<sect1 id="querysql-aliasreferences">
<title>Alias and property references</title>
<para>
The <literal>{cat.*}</literal> notation used above is a shorthand for "all properties". You
may even list the properties explicity, but you must let Hibernate provide SQL column aliases
for each property. The placeholders for these column aliases are the property name qualified by
the table alias. In the following example, we retrieve <literal>Cat</literal>s from a different
table (<literal>cat_log</literal>) to the one declared in the mapping metadata. Notice that we
may even use the property aliases in the where clause.
The <literal>{cat.*}</literal> notation used above is a shorthand for "all properties".
Alternatively, you may list the columns explicity, but even then you must let Hibernate
inject the SQL column aliases for each property. The placeholders for a column alias is
just the property name qualified by the table alias. In the following example, we retrieve
<literal>Cat</literal>s from a different table (<literal>cat_log</literal>) to the one
declared in the mapping metadata. Notice that we may even use the property aliases in the
where clause if we like.
</para>
<programlisting><![CDATA[String sql = "select cat.originalId as {cat.id}, "
+ " cat.mateid as {cat.mate}, cat.sex as {cat.sex}, "
+ " cat.weight*10 as {cat.weight}, cat.name as {cat.name}"
+ " from cat_log cat where {cat.mate} = :catId"
List loggedCats = sess.createSQLQuery(sql, "cat", Cat.class)
<programlisting><![CDATA[String sql = "select cat.originalId as {cat.id}, " +
"cat.mateid as {cat.mate}, cat.sex as {cat.sex}, " +
"cat.weight*10 as {cat.weight}, cat.name as {cat.name} " +
"from cat_log cat where {cat.mate} = :catId"
List loggedCats = sess.createSQLQuery(sql)
.addEntity("cat", Cat.class)
.setLong("catId", catId)
.list();
]]></programlisting>
.list();]]></programlisting>
<para>
<emphasis>Note:</emphasis> if you list each property explicitly, you must include all
@ -89,38 +100,45 @@ List loggedCats = sess.createSQLQuery(sql, "cat", Cat.class)
<para>
Named SQL queries may be defined in the mapping document and called in exactly the same way
as a named HQL query.
as a named HQL query. In this case, we do <emphasis>not</emphasis> need to call
<literal>addEntity()</literal>.
</para>
<programlisting><![CDATA[<sql-query name="mySqlQuery">
<return alias="person" class="eg.Person"/>
SELECT person.NAME AS {person.name},
person.AGE AS {person.age},
person.SEX AS {person.sex}
FROM PERSON person WHERE person.NAME LIKE 'Hiber%'
</sql-query>]]></programlisting>
<programlisting><![CDATA[List people = sess.getNamedQuery("mySqlQuery")
.setMaxResults(50)
.list();]]></programlisting>
<programlisting><![CDATA[<sql-query name="mySqlQuery">
<return alias="person" class="eg.Person"/>
SELECT {person}.NAME AS {person.name},
{person}.AGE AS {person.age},
{person}.SEX AS {person.sex}
FROM PERSON {person} WHERE {person}.NAME LIKE 'Hiber%'
</sql-query>]]></programlisting>
<para>
Using named SQL queries, you may also query for scalar values. To do this, use the type attribute
of the <literal>&lt;scalar-return&gt;</literal> element and specify a type there:
A named SQL query may return a scalar value. You must specfy the column alias
and Hibernate type using the <literal>&lt;return-scalar&gt;</literal> element:
</para>
<programlisting><![CDATA[<sql-query name="mySqlQuery">
<scalar-return column="name" type="string"/>
<scalar-return column="age" type="long"/>
<return-scalar column="name" type="string"/>
<return-scalar column="age" type="long"/>
SELECT p.NAME AS name,
p.AGE AS age,
FROM PERSON p WHERE p.NAME LIKE 'Hiber%'
</sql-query>]]></programlisting>
<para>
The <literal>&lt;return-join&gt;</literal> and <literal>&lt;load-collection&gt;</literal>
elements are used to join associations and define queries which initialize collections,
respectively. TODO!
</para>
</sect1>
<sect1 id="querysql-cud">
<title>Custom SQL for CUD</title>
<title>Custom SQL for create, update and delete</title>
<para>
Hibernate3 can use custom SQL statements for create, update, and delete operations.
@ -195,8 +213,8 @@ END updatePerson;]]></programlisting>
</sql-query>]]></programlisting>
<para>
This is just a named query declaration, as discussed earlier. You may reference this
named query in a class mapping:
This is just a named query declaration, as discussed earlier. You may
reference this named query in a class mapping:
</para>
<programlisting><![CDATA[<class name="Person">
@ -208,11 +226,10 @@ END updatePerson;]]></programlisting>
</class>]]></programlisting>
<para>
TODO: Document the following examples for collection loader and query-list
TODO: Document the following example for collection loader.
</para>
<programlisting><![CDATA[
<sql-query name="organizationEmployments">
<programlisting><![CDATA[<sql-query name="organizationEmployments">
<load-collection alias="empcol" role="Organization.employments"/>
SELECT {empcol.*}
FROM EMPLOYMENT empcol
@ -229,8 +246,7 @@ END updatePerson;]]></programlisting>
FROM EMPLOYMENT
WHERE EMPLOYER = :id AND ENDDATE IS NULL
ORDER BY STARTDATE ASC
</sql-query>
]]></programlisting>
</sql-query>]]></programlisting>
</sect1>

64
reference/en/modules/session_api.xml
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@ -856,6 +856,70 @@ secondSession.saveOrUpdate(mate); // save the new instance (mate has a null id)
</sect1>
<sect1 id="objectstate-replicating" revision="1">
<title>Replicating object between two different datastores</title>
<para>
It is occasionally useful to be able to take a graph of persistent instances
and make them persistent in a different datastore, without regenerating identifier
values.
</para>
<programlisting><![CDATA[//retrieve a cat from one database
Session session1 = factory1.openSession();
Transaction tx1 = session1.beginTransaction();
Cat cat = session1.get(Cat.class, catId);
tx1.commit();
session1.close();
//reconcile with a second database
Session session2 = factory2.openSession();
Transaction tx2 = session2.beginTransaction();
session2.replicate(cat, ReplicationMode.LATEST_VERSION);
tx2.commit();
session2.close();]]></programlisting>
<para>
The <literal>ReplicationMode</literal> determines how <literal>replicate()</literal>
will deal with conflicts with existing rows in the database.
</para>
<itemizedlist spacing="compact">
<listitem>
<para>
<literal>ReplicationMode.IGNORE</literal> - ignore the object when there is
an existing database row with the same identifier
</para>
</listitem>
<listitem>
<para>
<literal>ReplicationMode.OVERWRITE</literal> - overwrite any existing database
row with the same identifier
</para>
</listitem>
<listitem>
<para>
<literal>ReplicationMode.EXCEPTION</literal> - throw an exception if there is
and existing database row with the same identifier
</para>
</listitem>
<listitem>
<para>
<literal>ReplicationMode.LATEST_VERSION</literal> - overwrite the row if its
version number is earlier than the version number of the object, or ignore
the object otherwise
</para>
</listitem>
</itemizedlist>
<para>
Usecases for this feature include reconciling data entered into different database
instances, upgrading system configuration information during product upgrades,
rolling back changes made during non-ACID transactions and more.
</para>
</sect1>
<sect1 id="objectstate-flushing">
<title>Flushing the Session</title>